The proposed research is aimed at the understanding of the gene functions of Herpes simplex virus (HSV) involved in viral DNA synthesis, latency, and malignant transformation. Viral DNA replication will be investigated using the large number of viral mutants temperature sensitive for DNA synthesis. The overall scheme of HSV DNA replication will be studied by biochemically and electron microscopically characterizing replicating DNA and DNA-protein complexes from infected cells. The detailed mechanism of DNA chain growth will be approached using in vitro systems, such as isolated nuclei. In vitro complementation systems derived from mutant infected cells will be used to assay for and purify viral functions required for DNA replication. Model systems for latent HSV infections and malignant transformation by HSV will be studied by using existing cell lines, which are non-permissive for lytic infection by HSV. Attempts to establish new systems of this kind will be made using neuronal cell lines and differentiating teratocarcinomas.